Conventional hydraulic cylinders (hydraulic actuators, linear hydraulic motors) are mechanical devices that can provide reciprocating linear displacement power to submersible pumps, such as hydraulic diaphragm insert pumps (HDIs).
FIG. 1 shows a conventional hydraulic actuator 100 suitable for submersible pump applications. The conventional hydraulic cylinder 100 includes an outer cylinder piece known as the barrel 102, a sliding piston 104 inside the barrel 102, a piston rod 106 to transfer power from the piston 104 to an external submersible pump 108, and a central “feed” rod (“center rod”) 110 that slides in a cylindrical hole through a central longitudinal axis of the piston 104. The center rod 110, since it passes through the piston 104, provides hydraulic fluid through a hollow bore to the far side of the piston for retraction.
In conventional designs, the piston 104, piston rod 106, center rod 110, and other moving parts are over-constrained to strict and unforgiving linear displacement with no tolerance for misalignment, resulting in extra load and efficiency loss as the components struggle against each other along conflicting axes, forcing some elastic deformation, friction, power loss, and early wear of the parts.